Woody plants, such as trees and shrubs, are primary landscape plants. Once carefully selected and planted, it is desirable for the plants to grow to mature size and enhance the aesthetics in settings such as residences as well as parks, corporate campuses, university grounds, and boulevards.
In the popular mind, roots of woody plants, especially tree roots, grow deep and anchor a tree securely underground in a root pattern providing more or less a mirror image of the plant's above surface branch structure. Such a misconception is illustrated in FIG. 6 in the tree labelled A. The truth, however, is much different. Most tree species and other primary landscape plants do not have such tap roots. Even when species that are predisposed to tap roots, such as oaks, walnuts, and hickories, attempt to grow tap roots, root growth is dependent on soil conditions. Hard impenetrable soil tend to make these trees grow fibrous root systems instead of tap roots.
In the much more common fibrous systems, root growth occurs predominantly in a layer of about 18 inches below the ground surface as illustrated in FIG. 6 in the tree labeled B. Even more surprising, more than half of all root growth occurs in the top most 9 inches of soil. The root zone 100 does not end at the dripline 110, i.e. the maximum perimeter of the crown (as is commonly assumed), but spreads beyond this area. However, the root zone within the dripline 110 is the most critical part of the root zone 100 since the most significant rooting occurs within that area.
Unfortunately not all primary landscape plants are able to reach or maintain a healthy maturity. Root disorders are the leading cause of premature decline of woody plants that are the primary landscape plants. Root disorders cause over 80% of landscape plant failures. Arboriculture research suggests that the most significant limiting factor on root development is soil compaction. Soil compaction limits root growth and health because roots are unable to penetrate the compacted soil. Soil normally consists of solid particles of sand, clay, and silt and pores filled by water and/or air. Soil becomes compacted when the solid particles are packed together by reducing pore space.
Roots grow when soil conditions are favorable. Ideal growing conditions for plants exist when solids and pores are nearly equal in volume. A forest setting provides optimal growing conditions for roots. Debris, which is not cleared away in natural settings, forms pockets within the soil that maintain moisture and air in combination with the soil. The disintegrating debris provides nutrients, encourages growth of favorable mycorrhizae fungi, and protects from disease by promoting healthy growth. Most trees form a symbiotic relationship with mycorrhizae fungi. In return for nutrition from the host plant, mycorrhizae fungi increase the root's efficiency.
Soil compaction arises in certain soils and weather conditions, and where the soil is exposed to traffic. Soil compaction reduces the amount of organic matter, nutrition, and favorable fungi available to the roots. Even in serene settings such as parks, soil compaction often occurs because of construction activity during the establishment of the campus, pedestrian and service vehicle traffic during occupancy, athletic and recreational activity in landscaped areas, or incorrect landscaping practices.
Root growth will also be hampered by compacted soil because the soil retains an incorrect moisture content. Compacted soil can suffer from excessively high or excessively low moisture contents.
Compacted soil in low lying areas typically puddles rain water on the surface for some time after a downpour. Lacking sufficient porosity to efficiently percolate to groundwater levels, the water seeps throughout the soil filling available pores. The saturated soil encourages disease bearing microbes to attack both the favorable fungi and the roots. Even when roots are able to grow in compacted soil, root growth is generally lower than normal since mycorrhizae fungi may be inadequate present or the roots are under attack from disease.
In contrast, compacted soil in higher terrain may experience rain water run-off instead of percolation of water into the soil. Thus, even when rainfall is adequate for plant growth, the soil may be too dry, and the roots and favorable fungi can wither away.
Reviving woody plants that are in decline is usually preferred to replanting. Revival avoids costs for removal and additional costs for replacement. Additionally, the loss of trees or shrubs adversely impacts privacy, shade, noise reduction, aesthetics, and property values during the time it takes for replacements to regrow to the size of the removed plants.
Typically, revival has meant either aggressively fertilizing the subject plant or loosening the soil by laborious means. Fertilization may be accomplished by applying fertilizer on the ground surface and watering the plant. Revival success is dependent on the degree of soil compaction and existing moisture content. To reach roots directly, fertilizer may be injected as a water based solution into the rooting soil.
Other methods include laboriously exposing roots using trowels and small digging implements. Once exposed, the roots were reburied with new loose soil or covered with the existing soil now more loosened. This method is similar to the way archeologists dig for shards of pottery—slow and tedious.
An improvement over manual excavation is a vertical mulching technique where a grid of 1 to 2 inch holes is drilled in the rooting soil. The holes are then backfilled with porous material and/or fertilizer. This method has limited effectiveness because the beneficial effects are limited to the area where each hole is drilled, and mechanical excavation traditionally is not recommended since it easily damages sensitive plant roots. Another technique, radial trenching, involves using a small backhoe to loosen soil along radial lines extending for a distance from the tree trunk out to the dripline of the tree. However, this technique can be destructive and damage root systems.
A relatively new technique of soil loosening uses compressed air. Compressed air released at supersonic speed fractures the soil, with minimal damage to roots. Unlike porous soil, non-porous matter such as roots remain minimally damaged by the compressed air. The soil granules size after fracture is dependent on soil type, moisture content, and degree of compaction. Soil fracturing avoids the problems of mechanical excavation.
Fracturing soil by using compressed air is popularly used on lawns and turfs, such as golf courses. To maximize efficiency compressed air is injected in a grid. The grid is spaced so to aerate the soil evenly throughout a specified area by fracturing the soil. To keep the fractures open under continued usage of turf, fill material such as polystyrene pellets are forced into the soil with the pressurized air.
However, such method is inappropriate for a woody landscape plants because turf plants and woody landscape plants differ fundamentally. In fast growing turf plants, individual plants are intertwined. Thus if one plant dies, another quickly takes its place. However, woody landscape plants are more substantial and even when in grouped together fatal damages done to one is not easily corrected by natural instinct by other to take the place of the declining plant. Thus, to improve the rooting soil of woody landscape plants a method different from the one being used in other landscaping must be used.
Therefore, what is desired is a method of improving the rooting soil of a woody landscape plant.
What is also desired is a method of cost effectively improving the rooting soil of a woody landscape plant.
What is also desired is a method with an optional feature incorporating an expert system in the decision making process of improving the rooting soil of a woody landscape plant.